Substantial amounts of the oxides of nitrogen are formed in a turbine engine combustor when the flame temperature in any region exceeds about 3200.degree. F. In addition, excessive carbon monoxide is discharged if the local flame temperature falls below about 2500.degree. F. To reduce these noxious emissions to acceptable levels, it is desirable to operate the combustor in such a manner that the flame temperature does not exceed 3200.degree. F. or fall below 2500.degree. F. at any point. This can be accomplished by vaporizing the fuel before it is burned and adjusting the fuel-air ratio at each point in the burner so that the flame temperature does not exceed the limits. Unfortunately, the distribution of air leaving the compressor of a typical turbine engine is not uniform and flowrate varies substantially from point to point. In some engines, this variation exceeds 50% of the mean airflow. Moreover, the nonuniformity of the airflow changes with both changing engine operating conditions and the wear of engine compressor seals. Therefore, in order to prevent the local flame temperature from exceeding 3200.degree. F. on the high side or falling below the limit of about 2500.degree. F. on the low side as the local airflow changes, it is desirable to measure the flame temperature and adjust either the airflow or the fuel flow in each local region of measurement to maintain the desired flame temperature.
Again it is unfortunate that the flame temperature which is 3200.degree. F. during steady state operation and may exceed 4000.degree. F. during transients is above the practical operating range of most durable, immersion-type temperature sensors such as thermocouples. Some pseudo-temperature sensors operate on the basis of measuring a heat transfer rate from which a gas temperature is calculated. Because of the wide variations in heat transfer rate which occur with changes in engine operating condition, aircraft altitude and aircraft flight velocity, this type of sensor is inadequate for aircraft turbine engines.